Normal
Có:\[\\ \sqrt{3} \sin 2x.(2\cos x + 1) + 2 = \cos 3x + \cos 2x - 3\cos x\\ \Leftrightarrow \sqrt{3} \sin 2x.(2\cos x + 1) =\cos3x+\cos x+\cos2x-4\cos x-2\\ \Leftrightarrow \sqrt{3} \sin 2x.(2\cos x + 1) =2\cos x \cos2x+\cos2x-4\cos x-2\\ \Leftrightarrow (\sqrt{3} \sin 2x-\cos2x-2).(2\cos x + 1) =0\\ \Leftrightarrow \left(2\sin\left(2x-\frac{\pi}{6}\right)-2\right).(2\cos x + 1) =0\]................
Có:
\[\\ \sqrt{3} \sin 2x.(2\cos x + 1) + 2 = \cos 3x + \cos 2x - 3\cos x\\ \Leftrightarrow \sqrt{3} \sin 2x.(2\cos x + 1) =\cos3x+\cos x+\cos2x-4\cos x-2\\ \Leftrightarrow \sqrt{3} \sin 2x.(2\cos x + 1) =2\cos x \cos2x+\cos2x-4\cos x-2\\ \Leftrightarrow (\sqrt{3} \sin 2x-\cos2x-2).(2\cos x + 1) =0\\ \Leftrightarrow \left(2\sin\left(2x-\frac{\pi}{6}\right)-2\right).(2\cos x + 1) =0\]
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